Electrically operated aerosol-generating device with continuous power regulation

Abstract

An aerosol-generating device is provided, including an electrical power source; an electrical heater; and a power control circuit connected between the power source and the heater, the circuit including a power measuring unit configured to determine a power supplied to the heater from the power source and to output a power measurement voltage proportional to power supplied to the heater, a voltage comparator connected to the power measuring unit and configured to output a voltage difference signal based on a difference between the power measurement voltage and a reference voltage, and a power regulator connected between the power source and the heater and responsive to the voltage difference signal, the power regulator being configured to adjust a current or a voltage supplied to the heater in order to return the voltage difference signal to within a predetermined range or in order to minimize the voltage difference signal.

Claims

1. An aerosol-generating device, comprising: an electrical power source; an electrical heater; and a power control circuit connected between the electrical power source and the electrical heater, wherein the power control circuit is an analog circuit and comprises: a power measuring unit configured to determine a power supplied to the electrical heater from the electrical power source and to output a power measurement voltage proportional to power supplied to the electrical heater, a voltage comparator connected to the power measuring unit and configured to output a voltage difference signal based on a difference between the power measurement voltage and a reference voltage, and a power regulator connected between the electrical power source and the electrical heater and responsive to the voltage difference signal, the power regulator being configured to adjust a current or a voltage supplied to the electrical heater in order to return the voltage difference signal to within a predetermined range or in order to minimize the voltage difference signal, wherein the power measuring unit, the voltage comparator, and the power regulator are all implemented using analog circuit components.

2. The aerosol-generating device according to claim 1, wherein the power regulator is further configured to adjust the current supplied to the electrical heater only if the voltage difference signal is outside of the predetermined range.

3. The aerosol-generating device according to claim 1, wherein the power regulator comprises a bipolar junction transistor having a base connected to an output of the voltage comparator.

4. The aerosol-generating device according to claim 1, wherein the power measuring unit comprises a multiplier unit configured to multiply a voltage applied to the electrical heater with a voltage indicative of the current applied to the electrical heater to provide the power measurement voltage.

5. The aerosol-generating device according to claim 1, wherein the power measuring unit comprises a current measurement unit configured to provide an output voltage indicative of the current applied to the electrical heater.

6. The aerosol-generating device according to claim 1, further comprising a microcontroller configured to provide the reference voltage.

7. The aerosol-generating device according to claim 6, wherein the microcontroller is further configured to vary the reference voltage during operation of the aerosol-generating device.

8. The aerosol-generating device according to claim 7, wherein the microcontroller is further configured to vary the reference voltage based on a detected number of user inhalations.

9. The aerosol-generating device according to claim 7, wherein the microcontroller is further configured to vary the reference voltage based on time following activation of the aerosol-generating device.

10. The aerosol-generating device according to claim 1, wherein the aerosol-generating device is a handheld device.

11. The aerosol-generating device according to claim 1, wherein the electrical heater is removably coupled to the power control circuit and is configured to allow for replacement of the electrical heater.

12. The aerosol-generating device according to claim 1, wherein the aerosol-generating device is configured to generate an aerosol for user inhalation, and, in use, user inhalation draws air past the electrical heater, and wherein the aerosol-generating device comprises a memory and is configured to record changes in current or voltage supplied to the electrical heater as an indication of user inhalation.

13. A method for regulating a supply of power to an electrical heater in an electrically heated aerosol-generating system, the aerosol-generating system comprising an electrical power source, an electrical heater, and a power control circuit connected between the electrical power source and the electrical heater, wherein the power control circuit is an analog circuit, and wherein the power measuring unit, the voltage comparator, and the power regulator are all implemented using analog circuit components, the method comprising: determining a power supplied to the electrical heater from the electrical power source and generating a power measurement voltage proportional to power supplied to the electrical heater; generating a voltage difference signal based on a difference between the power measurement voltage and a reference voltage; and adjusting a current or a voltage supplied to the electrical heater in order to maintain the voltage difference signal within a predetermined range or in order to minimize the voltage difference signal.

Description

(1) Examples in accordance with the invention will now be described in detail, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic illustration of an electrically heated aerosol-generating system;

(3) FIG. 2 is a schematic illustration of the components of a power control system for an electrically heated aerosol-generating system in accordance with the invention;

(4) FIG. 3 is a circuit diagram of a power control system of the type shown in FIG. 2; and

(5) FIG. 4 is an example of a power profile for an electrically heated aerosol-generating system of the type shown in FIG. 1.

(6) In FIG. 1, the components of an embodiment of an electrically heated aerosol generating device 1 are shown in a simplified manner. Particularly, the elements of the electrically heated aerosol generating device 1 are not drawn to scale in FIG. 1. Elements that are not relevant for the understanding of this embodiment have been omitted to simplify FIG. 1.

(7) The electrically heated aerosol generating system comprises an aerosol-generating device 1 and an aerosol-forming substrate 2, for example a cigarette. The aerosol-forming substrate 2 is pushed inside the housing of the device 1 to come into thermal proximity with an electrical heater 40. The aerosol-forming substrate 2 will release a range of volatile compounds at different temperatures. By controlling the power supplied to the electrical heater, the release or formation of these volatile compounds can be controlled.

(8) Within the device 1 there is an electrical energy supply 60, for example a rechargeable lithium ion battery. Power control circuitry 100 is connected to the heating element 40 and the electrical energy supply 60. A microcontroller 70 is connected to the power control circuitry 100 and to the electrical energy supply.

(9) In this example, the heating element 40 is positioned on a rigid, blade-shaped substrate within the housing of the device. The blade-shaped substrate can penetrate the aerosol-forming substrate, which in this example is a cigarette. However, it should be clear that other forms of heating element can be used. In particular, the heating element may be positioned externally of the aerosol-forming substrate.

(10) In use, power is supplied to the heater to heat the aerosol-forming substrate. A user draws on a mouthpiece end of the aerosol-forming substrate to draw air past the heater and the aerosol-forming substrate. Compounds in the aerosol-forming substrate that have been vaporised by the heater and entrained in the airflow, cool to form an aerosol before entering the user's mouth.

(11) The basic elements of the power control circuitry 100 are shown schematically in FIG. 2 together with the battery 60 and the heater 40. The power control circuitry 100 comprises a current measurement unit 20, a power measurement unit 30, a voltage comparator 10 and a power regulator 12. The power regulator is configured to adjust the current or voltage applied to the heater 40 based on an output from the voltage comparator 10. The voltage comparator is configured to compare a reference voltage V.sub.ref with the output of the power measurement unit 30 and provide, as an output, a voltage representing a difference between V.sub.ref and the output of the power measurement unit 30. The power measurement unit is configured to measure the power supplied to the heater. The power measurement unit receives as inputs a voltage that is representative of the current that is applied to the heater 40 from the current measurement unit 20 and the voltage applied to the heater 40 by the power regulator. The power measurement unit provides as an output a voltage representative of the product of the input signals. The power regulator 12 is configured to act to minimise an output from the voltage comparator or to adjust the power applied to the heater 40 if the output from the voltage comparator is outside a predetermined range.

(12) FIG. 3 shows one embodiment of the power control circuitry of FIG. 2. A lithium ion battery 60 is connected to an electrical heater 40 through the power control circuit 100. The battery 60 generates a voltage V.sub.dc that gives rise to a current through the heater 40. The heater heats up as a result of the Joule effect. The power control circuit 100 measures the power applied to the heater and adjusts the power applied based on the measurement. The power control circuit comprises the same functional components as shown in FIG. 2.

(13) The power applied to the heater is determined by measuring the current using current measurement unit 20 and multiplying the measured current with the voltage applied to the heater. The current measurement unit comprises a resistor 201 of known electrical resistance connected in series with the electrical heater 40, and an operation amplifier 202. The current through the resistance 201 is equal to the current through the electrical heater 40. The current through the resistor 201 is equal to the voltage across the resistor 201 divided by its electrical resistance. The operational amplifier 202 is connected to the resistor 201 so that one input to the operational amplifier is connected to a high side of the resistor 201 and the other input to the operational amplifier is connected to a low side of the resistor 201. The output of the operational amplifier is therefore a voltage V.sub.l that is proportional to the current through the electrical heater 40. The output of the operational amplifier is connected to a multiplier 30, which is the power measurement unit. The other input to the multiplier 30 is the voltage V.sub.load across the heater 40.

(14) The output of the multiplier 30 is a voltage V.sub.measured, proportional to the power applied to the heater. This voltage is input to the voltage comparator 10. The voltage comparator 10 comprises an operational amplifier 101. The negative input to the operational amplifier 101 is V.sub.measured. The positive input to the operational amplifier is a reference voltage V.sub.ref. A microprocessor 70 provides a reference voltage V.sub.ref to the power control circuit. The microprocessor is powered by the battery 60.

(15) The output of the operational amplifier 101 is the difference between V.sub.measured and V.sub.ref, which is ΔV. A current limiting resistor 102 is provided between the output of the operational amplifier 101 and the power regulator 12 to limit the current flowing into the power regulator. Similarly a current limiting resistor 50 is connected in series with the heater 40 to limit the current through the heater 40.

(16) The power regulator is a NPN transistor 12. The output of the voltage comparator is connected to the base of the transistor 12. If ΔV is within a particular range, then the current through the transistor 12 will be unchanged. However if ΔV is positive (when V.sub.measured is less than V.sub.ref) and greater than a threshold value, then current through the transistor 12 is increased to increase power delivered to the heater 40. If ΔV is negative (when V.sub.measured is greater than V.sub.ref) and greater than a threshold value, then current through the transistor 12 is decreased to decrease power delivered to the heater 40. In this way the value of the supplied power is regulated and in particular is held within a particular range dependent on the value of V.sub.ref.

(17) The power control circuit 100 acts as a control loop and uses analogue components so that power regulation is continuous and does not require sampling. If V.sub.ref is constant then the power supplied to the heater will remain with a predetermined range.

(18) It is possible to adjust the power supplied to the heater 40 during operation of the device by adjusting the value of V.sub.ref. FIG. 4 illustrates one example of the way in which V.sub.ref could vary during operation of a device of the type illustrated in FIG. 1. At time t.sub.0 the device is activated by a user pressing an “on” button on the device. Initially V.sub.ref is set at a relatively high value in order to bring the heater 40 and aerosol-forming substrate 2 up to an operating temperature quickly. This is to allow a user to have a first puff as soon as possible. After a set time or based on a temperature measurement, at time ti, V.sub.ref is reduced to a lower value. This is to maintain the heater 40 at an operating temperature at which a desirable aerosol can be generated.

(19) It may be desirable to increase the power applied to the heater as the aerosol-generating substrate becomes depleted in order to ensure that an adequate amount of aerosol is produced for each puff. The power may be increased following each user puff or following a set number of user puffs. For example, as shown in FIG. 4, at time P.sub.1, after completion of three user puffs, V.sub.ref is increased. At times P.sub.2 and P.sub.3, corresponding to completion of fourth and sixth user puffs respectively, V.sub.ref is also increased. Alternatively, increases in V.sub.ref may be made simply at predetermined times after activation of the device.

(20) User puffs may be detected using a dedicated airflow sensor in the device. Alternatively, user puffs may be detected by monitoring changes in the electrical resistance of the heater 40. Airflow past the heater as a result of user puffs will have a cooling effect on the heater, leading to a change in the electrical resistance of the heater. A change in the electrical resistance of the heater will result in a change to V.sub.load and correspondingly an increase in V.sub.l. By monitoring V.sub.load or V.sub.l the start and end of user puffs can be detected. This information can be used to trigger changes in the reference voltage V.sub.ref.

(21) While the control circuit has been described with reference to the device illustrated in FIG. 1, it should be clear that it is applicable to other types of aerosol-generating device. In particular, it may be used in devices that have a heater positioned externally of an aerosol-generating substrate. For example, the heater 40 may be implemented as a flexible heater that surrounds a cavity in an aerosol-generating device, where the cavity is configured to receive an aerosol-forming substrate. In another example, the aerosol-generating device may be integral with the aerosol-forming substrate and designed to be disposed of when the aerosol-forming substrate is exhausted. In a further example, the heater 40 may be provided together with the aerosol-forming substrate in a disposable cartridge, with the power source and power control circuit provided in a reusable main unit.

(22) Furthermore, while the control circuit has been described with reference to a device that supplies power to a heater continuously during operation of the device, it is applicable to devices configured to supply power to a heater only during user puffs or inhalations. For example, the microprocessor may be configured to provide a V.sub.ref of zero until a user puff is detected by a puff sensor in the device, and then to provide a positive value of V.sub.ref for a set time period, say two seconds, following detection of the user puff, before returning to a V.sub.ref of zero until the next user puff is detected. The value of V.sub.ref may change from puff to puff.